The present invention relates generally to the field of optical communications, and more specifically, the present invention discloses a method and apparatus for terminating optical links in an optical add-drop multiplexer (OADM).
Optical wavelength division multiplexing (WDM) techniques are increasingly being employed in fiber optic communication systems. WDM systems transmit information signals over optical fibers using optical signals of different wavelength, often referred to as carrier signals. Thus, WDM techniques allow a significant number of information signals to be transmitted over a single optical fiber.
While such WDM techniques provide substantially higher fiber bandwidth utilization, such WDM techniques suffer from a number of limitations, which, if overcome, could further improve the performance and bandwidth utilization of such WDM systems. Fiber optic communications networks are typically arranged in a number of topological configurations. For example, a fiber optic network can consist of two terminals communicating data over an optical link. As additional terminals are included in an optical network, they may be linked in a daisy-chain configuration in series by a plurality of optical links. Alternatively, ring configurations can also used, as well as other two-dimensional networks. Bidirectional optical links between two terminals typically include a plurality of optical fibers to provide redundancy in the event of a failure in an optical fiber.
A number of techniques have been proposed or suggested for routing an optical signal at a given node, based on wavelength. Optical networks often include optical add-drop multiplexers (OADM) having one or more input and output fibers, where an incoming optical signal may either be passed through the node or routed to a local destination, based on its wavelength. In order to allow the optical network to be dynamically reconfigured, all fibers are currently terminated at each node (i.e., at the end of each link) in the optical network, and the signal is restored at the beginning of each link. Such forced termination at each node, however, unnecessarily increases system costs. A need therefore exists for a new method and apparatus for terminating optical links in an optical network that reduces system costs and maintains satisfactory quality levels of the optical line system (OLS) at the output of such nodes.
Generally, a method and apparatus are disclosed for terminating optical links in an optical network. The present invention recognizes that while the forced termination of the protection ring at each node is generally desirable to permit dynamic reconfiguration of the protection ring in the event of a failure, such forced termination is not necessary on the working ring and unnecessarily increases system cost. Thus, in accordance with the present invention, each node forces the termination of the received optical signals only on the protection ring and does not force termination on the working ring unless necessary.
According to one aspect of the invention, a signal on an end-to-end light path on the working ring is terminated only when required by engineering rules, such as signal-to-noise requirements. Specifically, the present invention does not force terminate an end-to-end light path on the working ring at a given node (or on a link between two nodes) unless the signal will fail to meet certain criteria, such as a minimum optical signal-to-noise ratio, at the next node.